Just to tell my experience with Freerider to serve as a warning to people having the same issues.
I have a Futaba Radio (FC 18) connected to the PC ( Windows 10 64bits) through an Aerosim RC dongle.
I have not used Freerider for a long time and today I have played again. To my surprise it did not work as it did before with the Futaba-Aerosim dongle combination.
After some reading through these posts and some investigation I eventually realized that I have installed a virtual USB Joystick driver ( VJoy ) which was the cause of Freerider not reading correctly the inputs from the Futaba radio.
You can disable/uninstall Vjoy or any other virtual Joystick in Windows Device Manager to solve the issue. After disabling Vjoy everything is working as before.
Hope it be of any help.